Syrian troops on Monday battled with rebel groups close to the armistice line with Israel in the Golan Heights, as the UN pursued efforts to free 44 peacekeepers held by insurgents.

The unrest on Israel's doorstep followed a spillover of mortar and gunfire into Israeli-controlled territory, putting Tel Aviv on high alert and prompting it to shoot down a drone over the occupied plateau on Sunday.

Several mortar rounds struck on the edges of the ceasefire line early on Monday, as the combatants exchanged rocket, mortar and tank fire near the Quneitra crossing, which Al-Qaeda-linked rebels seized last week, an AFP correspondent reported.

Israel had closed off the area around the crossing after an officer was wounded by stray fire last Wednesday when insurgents led by the Al-Nusra Front took over the crossing into the Israeli-occupied sector of the Golan.

The Syrian Observatory for Human Rights, a Britain-based monitoring group, said Nusra fighters were locked in fierce clashes with government troops for control of the Hamidiyeh area in Quneitra, the army's remaining stronghold there.

Al-Watan newspaper, which is close to the Syrian regime, said the army was "confronting attempts by Al-Nusra fighters and other terrorist groups" to take control of Hamidiyeh.

Meanwhile the UN was working to locate and release 44 Fijian peacekeepers whom the insurgents captured while they overran Quneitra, as 72 Filipino members of the same force escaped a rebel siege on their positions nearby.

The Fijians were "safe" but their whereabouts uncertain, a military official said Saturday, indicating there was contact with the group that was holding them.

And after a seven-hour firefight, 40 Filippino peacekeepers slipped away under cover of night after rebels rammed their Golan Heights outpost with armed trucks, the Philippine military said Sunday.

More than 30 other Filippino troops had reached safety on Saturday.

Israel watches warily

Israel said it shot down a drone over an area under their occupation, with the army warning in a statement it would "respond to any violation of our sovereignty."

Defence Minister Moshe Yaalon toured the region on Sunday, as the army sent reinforcements along the armistice line and deployed armoured troop carriers, an AFP photographer said.

Yaalon warned that Israeli "tolerance" should not be tested.

"These past weeks we have proven that our tolerance is minimal when our integrity is struck, either intentionally or unintentionally," he said.

There has been repeated fire across the ceasefire line since the uprising in Syria erupted in March 2011, not all of it stray.